Mining_Methods_UnderGround_Mining - Mining and Blasting
Mining_Methods_UnderGround_Mining - Mining and Blasting
Mining_Methods_UnderGround_Mining - Mining and Blasting
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keMi, Finl<strong>and</strong><br />
Kemi underground mine – simplified long section.<br />
produced from open pits, resulting in<br />
130 million t in the waste heaps.<br />
Ore grade control<br />
Ore grade control in both the open pit<br />
<strong>and</strong> the underground mine involves intensive<br />
wire line diamond core drilling,<br />
to determine boundaries <strong>and</strong> qualities<br />
of specific ore types. In addition, all<br />
blast holes in the open pit are sampled.<br />
Technical innovations for ore characterization<br />
<strong>and</strong> quantification include<br />
OMS-logg down hole logging, <strong>and</strong> automated<br />
image analysis for establishing<br />
grain size distribution.<br />
Basic production data about mineralogical<br />
<strong>and</strong> process histories are logged<br />
Atlas Copco Diamec U6 APC at work underground.<br />
for each ore stope on a daily basis, <strong>and</strong><br />
this is merged <strong>and</strong> compared with daily<br />
<strong>and</strong> blast-specific production histories<br />
from the database.<br />
Each ore blast is treated selectively at<br />
the concentrator, in order to minimize<br />
feed variation <strong>and</strong> maximize process<br />
stability.<br />
In the concentrator, total chromite<br />
recovery is around 80%, depending on the<br />
proportion of lumpy ore. Metallurgical<br />
grade concentrate contains about 45%<br />
Cr 2O 3 of 0.2 mm grain size, while upgraded<br />
lumpy ore is about 35% Cr 2O 3<br />
with 12-100 mm size. The former is pelletised<br />
at Tornio, <strong>and</strong> then mixed with<br />
upgraded lumpy ore before smelting to<br />
produce ferrochrome.<br />
Concentrator operation is optimized<br />
by accurate calibration of the feed slurry<br />
analyzers, <strong>and</strong> control of product quality<br />
from each unit process, both by com-<br />
pensating for changes in feed type, <strong>and</strong><br />
measuring product quality on-line.<br />
Manual input can be used, as well as<br />
on-line information.<br />
A Craelius Diamec 264 APC drill rig<br />
carries out 10 km of coring each year.<br />
Drill sections are established every 10<br />
m <strong>and</strong> downhole survey is st<strong>and</strong>ard procedure,<br />
using a Maxibore system. Based<br />
on the drill hole data, a 3D model of the<br />
orebody is created <strong>and</strong> used as a basis<br />
for production planning. Tying all these<br />
streams of collected data <strong>and</strong> planning<br />
outputs together requires an extremely<br />
fast communications network, interfacing<br />
with a single master database.<br />
underground infrastructure<br />
The main decline starts at a portal in<br />
the footwall side of the pit, at about 100<br />
m below the rim. The decline is mostly<br />
8 m-wide x 5.5 m-high, to accommodate<br />
passing vehicles. It descends at 1:7<br />
to a depth of 600 m at the base of the<br />
hoisting shaft, <strong>and</strong> connects with several<br />
intermediate sublevels. The decline<br />
is asphalted throughout most of its<br />
length.<br />
There is also a 5,000 cu m repair<br />
shop for open pit equipment at the 115 m<br />
level, <strong>and</strong> a larger 14,000 cu m workshop<br />
at the 350 m level for the underground<br />
mobile equipment fleet. The<br />
final 23,000 cu m main workshop is at<br />
the 500 m level. The 350 m level workshops<br />
are enclosed by megadoors, which<br />
keep in the heat so that an ambient 18<br />
degrees C can be maintained. The service<br />
bay is equipped with a 10 t travelling<br />
gantry <strong>and</strong> 16 m-long inspection<br />
pit. The washing bay is equipped with<br />
two Wallman hydraulically controlled<br />
washing cages, so there is no need for<br />
operatives to climb onto the mobile<br />
equipment.<br />
The main pumping station is located<br />
at the 350 m level, <strong>and</strong> has pumping<br />
capacity of 2 x 250 cu m/h. The slurrytype<br />
pumps, with mechanical seals,<br />
pump the unsettled mine water to the<br />
surface with a total head of 360 m. Two<br />
other dewatering pumping stations are<br />
located at the 500 m <strong>and</strong> 580 m levels.<br />
64 underground mining methods